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Researchers led by Dr. Mira Katan of Columbia University Medical Center conducted a study of chronic infections on 1,625 adults around age 70, all residents of northern Manhattan, which was published in the March 26 issue of the journal Neurology.

Participants completed a cognitive assessment called the Mini-Mental State Examination (MMSE), which measures attention, memory, and language skills in order to screen for dementia. Their blood samples were also tested for several common infections, including herpes simplex type 1 virus (HSV-1), which causes cold sores; herpes simplex type 2 (HSV-2), which causes genital herpes; cytomegalovirus; chlamydia pneumoniae, a common respiratory infection; and Heliobacter pylori, a type of stomach bacteria. The amount of exposure to the viral and bacterial pathogens was called "infectious burden."

Participants with a higher infectious burden were 25 percent more likely to score below average on cognitive tests. Researchers tried accounting for other factors that could have affected their cognitive function, like age, education, and drug and alcohol use, but the results still held.

The study found no association between infectious burden and decline in cognitive scores over time, implying that the damage caused by infections does not progress over a prolonged period.

The link between infections and cognitive impairments was highest among several demographic groups: women, people with lower education, and people with low levels of exercise.

Infections can amplify the body's inflammatory response over time, which Dr. Katan's previous research has tied to cognitive impairment and stroke. Exercise can reduce inflammation, which could explain why sedentary people showed greater cognitive impairment than those who exercised regularly.

Dr. Nunzio Pomara of the Nathan S. Kline Institute for Psychiatric Research in Orangeburg, New York, who was not involved in the study, told MyHealthNewsDaily that he was "quite happy to see that, at least in some instances, there could be a potentially treatable [cause of] cognitive dysfunction."

In a press statement, Dr. Katan stressed that this study only shows an association between cognitive impairment and infectious burden, though it is a strong one. More research is needed to replicate these results.

The study lends credence to the microbe-dementia hypothesis, detailed in an editorial in the same issue of Neurology, which suggests that microbial infections can cause cognitive impairments and dementia as a result of long-term damage to brain tissue.